Packers and bridge plugs are used to isolate zones in a subterranean location. Retrievable versions of such devices need to be released from sealing and mechanical grips that their components have on the surrounding wellbore. Different types of tools have been developed for such retrieval operations. Some are tubing run and others are delivered on wireline. Generally these tools need to grip and undermine the slips and sealing element that had earlier been set, most likely by compressive forces based on hydraulic pressure or setting down weight, for example.
The set isolation devices can have large pressure differentials acting on them and it is desirable to equalize pressure across such barrier devices before the slips and sealing elements are allowed to relax. Prior designs that have actually employed an equalizing pressure feature before release have done so in one continuous motion where it was hoped that the equalization had sufficiently taken place before the mechanical release. However, since both movements were supposed to be accomplished in the same unidirectional movement, there was a risk that the equalization had not sufficiently taken place by the time the mechanical release took place. If that happened the packer or plug could be propelled and get stuck at another location in the wellbore. If the retrieval tool was run in on tubing, the tubing could be bent and contorted as the packer or bridge plug that had not been fully equalized was propelled uphole upon mechanical release.
Some retrieval tool designs just grabbed the packer or bridge plug and mechanically released it without concern of differential pressure that may be acting on it at the time. Tools using a single jarring motion to release either with or without equalizing and run on wireline or tubing include: US Publication 2009/0000792; U.S. Pat. Nos. 7,036,602; 7,389,823; 4,805,699 (coiled tubing); 4,869,325 (coiled tubing); 6,220,348 (equalize and pull retrieval lugs); 6,244,642 (equalize and pull on retrieval lugs); 5,366,012 (jar and release); 3,714,983 (jar to equalize and release in same motion); 4,044,826 (jar and release); 3,667,543 (jar and operate a j-slot); 6,681,858 (tubing conveyed grapple) and 4,332,410 (release tool jars to break free of stuck packer).
What is needed in a retrieving tool and provided by the present invention is a way to be sure that the operation of equalizing a packer or bridge plug is done at a time and in a way that cannot release the slips and sealing element. More particularly the equalization and subsequent release for retrieval are accomplished with jar movements and intervening pickup force. The equalizing releases a locking dog on a second sleeve whose movement then becomes possible to release the packer or bridge plug and retrieve it. These and other features of the present invention will become more apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined from the literal and equivalent scope of the appended claims.